Pneumatically activated nail driving device

ABSTRACT

A fastener driving device particularly suited for use as a component of a production machine, the device embodying a housing structure configured so as to permit a pair of such devices to be mounted in either abutting or lapped relation to simultaneously drive two fasteners on centers spaced as close as 1 1/4 inches apart, the device embodying an improved mechanism for feeding successive nails from a large coiled package initially into a nail severing position from which position successive nails are separated from the package and then moved into a nail feeding position and then finally into a driving position within the drive track during one operative cycle so as to be driven in the next, the device also embodying a pneumatically actuated piston and cylinder unit of large capacity interconnected with the fastener driving element through an improved linkage arrangement which decreases the velocity and increases the force of the driving piston transmitted to the fastener driving element throughout the drive stroke, the driving piston being provided with an improved prestressed bumper assembly for resiliently arresting the moving parts at the end of the drive stroke.

United States Patent Maynard PNEUMATICALLY ACTIVATED NAIL DRIVING DEVICE [75] Inventor: George A. Maynard, Coventry, R1.

[73] Assignee: Textron Inc., Providence, R.I.

[22] Filed: July 29, 1971 [21] Appl. No.: 167,414

[52] U.S. Cl. 227/130, 227/136 [51] Int. Cl. B25c 1/04 [58] Field of Search 227/98, 130, 136, 227/138, 139

[56] References Cited UNITED STATES PATENTS 3,524,576 8/1970 Bader 227/136 2,354,841 8/1944 Shaft 227/130 3,281,046 10/1966 Boulay 227/136 X 1,845,186 2/1932 Raeburn 227/138 X 2,701,360 2/1955 Lang 227/138 X 2,994,879 8/1961 Shearer 227/130 3,396,572 8/1968 Godsey..... 227/51 X 3,480,193 11/1969 Ralston 227/130 3,612,381 10/1971 Schmidt 227/18 frimary Examiner-Granville Y. Custer, Jr.

Attorney-Cushman, Darby & Cushman [5 7 ABSTRACT A fastener driving device particularly suited for use as a component of a production machine, the device embodying a housing structure configured so as to permit a pair of such devices to be mounted in either abutting or lapped relation to simultaneously drive two fasteners on centers spaced as close as 1% inches apart, the device embodying an improved mechanism for feeding successive nails from a large coiled package initially into a nail severing position from which position successive nails are separated from the package and then moved into a nail feeding position and then finally into a driving position within the drive track during one operative cycle so as to be driven in the next, the device also embodying a pneumatically actuated piston and cylinder unit of large capacity interconnected with the fastener driving element through an improved linkage arrangement which decreases the velocity and increases the force of the driving piston transmitted to the fastener driving element throughout the drive stroke, the driving piston being provided with an improved prestres sed bumper assembly for resiliently arresting the moving parts at the end of the drive stroke.

26 Claims, 8 Drawing Figures PMENIEIJnuveo Ian 3.773.239

INVENTOR My ATTORNEYS PATENIH] NOV 20 3975 /& 14 z 75 ATTORNEYS PNEUMATICALLY ACTIVATED NAIL DRIVING DEVICE This invention relates to fastener driving devices and more particularly to pneumatically actuated fastener driving devices particularly constructed for use in production machinery as distinguished from portable manually operated fastener driving devices.

The art relating to portable pneumatically actuated fastener driving devices is highly developed. Devices of this type are constructed so as to be conveniently held in the hand of an operator and actuated in response to a manual actuation as, for example, by digitally squeezing a trigger or by a concommitant trigger squeeze and manual movement of the nosepiece of the device into contact with the workpiece into which a fastener is to be driven. Devices of this type have been embodied in production machinery but in general the characteristics which make them suitable for manual portable operation do not provide maximum efficiency when used in production machinery.

Accordingly, it is anobject of the present invention to provide a pneumatically operated fastener driving device of the type described which is of simple and rugged construction providing a nosepiece from which successive fasteners are driven which is relatively narrow, permitting a plurality of devices to be mounted on the frame of a production machine in closely spaced side-by-side relation and yet permitting simple access to the nosepiece for purposes of loading and clearing jams or the like.

Another object of the present invention is the provision of a pneumatically actuated fastener driving device of the type described having a driving piston and cylinder unit of a size to provide ample power to accomplish reliable operation for an extended period of time and an improved linkage system for connecting the piston rod of the power unit to the fastener driving element so as to effect movement of the fastener driving element through its drive stroke in response to the movement of the piston of the power unit through its drive stroke at a speed which decreases and with a force which increases with respect to the speed and force of the piston drive stroke as the fastener driving element approaches the completion of the drive stroke.

Another object of the present invention is the provision of a pneumatically actuated fastener driving device of the type described having improved prestressed bumper means for arresting the movement of the movable parts of the device as the fastener driving element approaches the completion of the drive stroke thereof.

Still another object of the present invention is the provision of a pneumatically actuated fastener driving device of the type described having an improved nail feed mechanism operable to advance the leading nail of a high capacity coil of nails into a severing position, the nail in the severing position being severed from the coil and moved downwardly into a feed position adjacent the drive track by the fastener driving element during the drive stroke thereof, the nail in the feed position being moved into the drive track near the end of the return stroke of the fastener driving element.

Still another object of the present invention is the provision of a pneumatically actuated fastener driving device of the type described which is simple in construction, capable of reliable automatic remote control operation and economical to manufacture and maintain.

These and other objects of the present invention will become more apparent during the course of the following detailed description and appended claims.

The invention may best be understood with reference to the accompanying drawings wherein an illustrative embodiment is shown.

In the drawings:

FIG. 1 is a side elevational view of a fastener driving device embodying the principles of the present invention;

FIG. 2 is a top plan view of the device showing two positions within which the device may be arranged with a similar device;

FIG. 3 is a vertical sectional view of the device showing the parts in the position assumed prior to the drive stroke;

FIG. 4 is a view similar to FIG. 3 showing the parts in an intermediate position during the drive stroke;

FIG. 5 is a sectional view taken along the line 55 of FIG. 1;

FIG. 6 is a fragmentary sectional view taken along the line 66 of FIG. 5;

FIG. 7 is a fragmentary sectional view taken along the line 7-7 of FIG. 4; and

FIG. 8 is a fragmentary sectional view taken along the line 88 of FIG. 4.

Referring now more particularly to FIGS. 1 and 2 of the drawings, there is shown therein a pneumatically actuated fastener driving device, generally indicated at 10, embodying the principles of the present invention. The device 10 comprises a housing structure, generally indicated at 12, defining an elongated drive track, gen- 7 erally indicated at 14, within which a fastener driving element 16 is mounted for successive cycles of operation, each including a drive stroke and a return stroke. A fastener feeding mechanism, generally indicated at 18, is provided in the housing structure 12 for feeding successive fasteners from a package supply of such fasteners into the drive track 14 to be driven by the fastener driving element outwardly of the drive track into a workpiece during the driving stroke of the fastener driving element. In order to effect successive operating cycles of the fastener driving element 16 there is provided a pneumatically actuated piston and cylinder unit, generally indicated at 20, which is connected with the fastener driving element 16 through a linkage, generally indicated at 22.

In the drawings, the device 10 is shown oriented so as to drive a fastener vertically downwardly into a horizontally disposed workpiece. It will be understood that the device 10 is particularly adapted to be mounted on the frame of a piece of production machinery and while the device would normally be mounted on the frame in the position shown, the device is capable of operating in any position other than the vertical position shown. With the above in mind, for convenience, the device will be described in relation to the orientation illustrated, and consequently terms such as horizontal", vertical, above, below, forward, rearward, etc. as used herein are to be construed in their relative sense.

The housing structure 12 may take a variety of different forms, however the structure illustrated in the drawings is preferred since it provides an especially rugged and durable assembly suitable for continuous production type reliable operation over an extended period of time. In the embodiment shown, the housing structure includes a first side member 24 in the form of a relatively thick plate of metal. The side member 24 is mounted in side-by-side relation with a pair of spaced upper and lower side members 26 and 28 fixedly secured to the side member by any suitable means such as bolts or the like. Mounted between the rearward portions of the upper and lower fixed side members 26 and 28 for movement between an operative position in side-by-side relation with the side member 24 and an open access position is a rearward access member 30. A forward nose piece housing member 32 is mounted in cooperating relation to the forward portion of the side member 24 and to the movable member 30 for movement into and out of an operative position with respect thereto.

As best shown in FIG. the movable member 30 is mounted for upward swinging movement from its operative position into its open access position. To this end, the upper end of the member 30 is formed with an extension 34 at its upper end which is positioned within a recess 36 formed in the lower surface of the fixed upper side member 26. A pivot shaft 38 extends through the extension 34 and has its ends engaged within vertically elongated openings 40 formed in the portions of the fixed side member 26 defining the ends of the recess 36. The movable side member 30 is resiliently urged into a position wherein the shaft ends are disposed in the bottom portion of the openings 40, by any suitable means, such as a coil spring 42 mounted within a bore 44 formed in the portion of the fixed side member 26 defining the side of the recess 36. Preferably, a plug 46 is disposed within the end of the bore with its lower end in engagement with the upper arcuate surface of the extension 34 and its upper end in engagement with the lower end of the spring 42.

The lower edge of the movable member 30 is relieved along its outer edge, as indicated at 48, and the upper edge of the lower fixed side member 28 is relieved along its inner edge, as indicated at 50, so as to provide cooperating edges which retain the movable member 30 in its operative position. Fixed to the outer surface of the movable member 30 is a knob 52 providing a means by which the operator can effect the movement of the movable member 30 from its operative position into its open access position. This movement is obtained by the operator initially moving the member 30 upwardly against the action of the spring 42. until the cooperating edge structures 48 and 50 clear one another after which the knob is pulled outwardly to swing the lower portion of the member 30 outwardly and upwardly about the axis of the pin 38.

As best shown in FIGS. 1 and 6, the removable nose piece member 32 is preferably in the form of an elongated vertical block having an L-shaped attaching flange or tongue 54 extending laterally from theforward portion thereof intermediate its ends. The adjacent outer surface of the side member 24 is formed with an L-shaped recess 56 of a size and shape to receive the attaching flange 54. The removable nose piece member 32 is moved into its operative position by an initial lateral movement of the attaching flange 54 through the recess 56 and a final rearward movement. The rearward outer edge of the nose piece member 32 is formed with an L-shaped vertically elongated recess 58 within which a cooperating L-shaped attaching flange 60 formed on the forward outer edge of the movable member 30 is adapted to engage when both of the members 30 and 32 are disposed in their operative positions.

It will be understood that the interior of the side member 24 and the interior of the upper fixed member 26 and nose piece member 32 are formed with mating cooperating vertical grooves which define the drive track 14 within which the fastener driving element 16 is mounted for reciprocal movement.

The fastener feeding mechanism 18 is particularly constructed to accommodate a multiplicity of common nails secured together by a pair of parallel wires welded to the shanks of the naiis, the multiplicity of nails being formed into a coil formation, all in accordance with the disclosure of commonly assigned Peterson US. Pat. No. 3,083,369

It will be understood, however, that other nail packages may be accommodated. A coil formation package is preferred since a great number of nails can be embodied in a single package resulting in less down time for reloading. In operation, a reel device (not shown) serves to support the main coil of the package with the leading portion thereof extending into the fastener feeding mechanism 18.

In order to guide the leading portion of the nail package from the coil, the nail feeding mechainsm 18 includes a pair of rollers 62, each rotatably mounted on a vertically extending shaft 64 having its ends journaled in the rearward end portions of a pair of upper and lower mounting arms 66. The forward ends of the mounting arms 66 are secured to the exterior surfaces of the side member 24 and movable side member 30 respectively. As best shown in FIG. 6, the ends of the shafts 64 are mounted within laterally outwardly opening slots formed in the ends of the arms 66, the outer ends of the slots being closed by suitable leaf springs 68 which serve to resiliently urge the rollers 62 toward one another and permit yielding movement of the two rollers 62 away from each other. With this arrangement, positive guiding of the leading portion of the nail package between the rollers is assured, the rearward periphery of the rollers insuring an accurate guiding movement of the leading portion of the package irrespective of the position of the production machine frame of the reel supporting the main coil of the nail package.

The rollers 62 are cylindrical in form and preferably are formed of a resilient material. The vertical extent of the rollers is such as to accommodate the shanks of the nails with the heads thereof disposed above the upper surface of the rollers. The interior surface of the side member 24 extending forwardly from the rollers 62 is formed with a horizontally extending nail head receiving slot 70 and a recess therebelow defining a shank engaging surface 72. Parallel horizontally extending slots 74 may be formd in the surface 72 to accommodate the connecting wires of the nail package. The nail engaging slot and upper portion of the shank engaging surface 72 extend forwardly and terminate in a position spaced rearwardly of the rearward surface of the fastener driving element 16 a distance sufficient to accommodate a single nail therebetween.

niently referred to as a nail severing position. In this regard, it will be noted that the rearward surface of the fastener driving element is concavely arcuate, as indicated at 76 in FIG. 7, to accommodate the nail head and shank of the nail disposed in the severing position.

The means for advancing the leading nail into the severing position is preferably in the form of a ratchet mechanism including a feeding pawl member 78 and a pair of holding pawl members 80. These pawl members are preferably mounted within the side member 24 permitting easy access thereto by movement of the access member 30 into its access position. The lower forward portion of the shank engaging surface 72 is formed with a relatively deep recess, indicated at 82, within which the feeding pawl member 78 is mounted for successive operative cycles, each including a forward feed stroke and a rearward return stroke.

In order to effect movement of the feeding pawl member 78 through successive operative cycles, the lower end portion of the feeding pawl member 78 is connected for movement with an actuating member 84. As best shown in FIG. 5, the actuating member 84 includes a lower rearward block portion which is horizontally slidably mounted within a horizontally extending guideway formed by correspondingly shaped cooperating grooves 86 formed in the interior surface of the lower portion of the side member 24 and the lower fixed member 28. Any suitable means may be provided for effecting the movement of the actuating member 84 through successive operative cycles. In the preferred embodiment shown, the actuating member is biased for movement forwardly by suitable spring means, such as a compression coil spring 88 having its forward end engaged within a bore opening rearwardly in the block portion of the actuating member 84 and its rearward end engaged within a forwardly opening bore formed in a plug member 90 suitable secured in the rearward portion of the grooves 86.

To further assist in effecting the feeding stroke of the actuating member 84 there is provided a second compression coil spring 92, the rearward end of which is disposed in engagement with a transverse plate 94 secured across the rearward edges of the members 24 and 28. The forward end of the coil spring 92 engages an upstanding lug portion 96 formed on the actuating member 84, the latter including a horizontally spaced forward lug portion 98. The feeding pawl member 78 has its lower end disposed between the lug portions 96 and 98 and connected with the actuating member 84 for pivotal movement about a horizontal axis extending fore and aft, as by a shaft 100 extending through the lug portions and the associated lower portion of the pawl member 78.

The upper portion of the feeding pawl member includes a pluralitiy of transversely extending feeding surfaces 102. These surfaces are positioned to engage the trailing surfaces of the nail shanks disposed within the feed path when the feeding pawl member is disposed in an operative limiting position of pivotal movement with respect to the actuating member 84. As best shown in FIG. 5, the feeding pawl member is biased into its operative limiting position by a spring pressed plunger assembly 104. The plunger assembly is of conventional construction and includes a plunger 106 resiliently urged into engagement with the pawl member 78, as by a coil spring 108.

During the movement of the leading nails with the feeding pawl member 78, the nail adjacent to the leading nail is moved past the holding pawls 80. In this regard, it will be understood that the interior surface of the access member 30 is appropriately contoured to guide the leading nails of the package along a straight I feed path when the access member is disposed in its operative position.

Each of the holding pawls is preferably in the form of a plunger assembly similar to the assembly 104, including the holding pawl member and a spring 1 l0 resiliently urging the latter outwardly into the path of movement of the nail shanks. As the nail moves by the holding pawl members 80, the latter are cammed inwardly against the action of springs 110 until the nail passes after which the springs serve to resiliently move the holding pawl members back into their operative position within the feed path so as to prevent rearward movement thereof.

In the embodiment shown, the actuating member 84 is moved through its return stroke, against the action of springs 82 and 92, by engagement of the fastener driving element 16 therewith during the drive stroke of the latter. To this end, the upper forward portion of the actuating member 84 and the lower rearward portion of the fastener driving element 16 are formed with cooperating cam surfaces 112 and 114 respectively. This arrangement insures positive movement of the actuating member 84 through its operating cycle in timed relation with the movement of the fastener driving element 16 through its operating cycle. It will be understood, however, that it is within the contemplation of the present invention to provide means other than cooperating cam surfaces for effecting movement of the actuating member through its return stroke as, for example, an auxiliary piston and cylinder unit or the like.

Extending rearwardly from the fastener driving element 16 at a position above the upper end of the rearward surface 76 thereof is an abutment providing a downwardly facing surface 116 for engaging the head of a nail disposed within the aforesaid severing position during the drive stroke of the fastener driving element. As best shown in FIG. 4, after an initial movement of the fastener driving element through its drive stroke, the surface 116 engages the head of the nail in the nail severing position so that the nail is carried downwardly with the fastener driving element during the subsequent movement thereof through its drive stroke. During the initial movement of the nail with the fastener driving element, the wires connecting the nail with the next adjacent nail are severed and the nail is finally moved downwardly into a feeding position rearwardly adjacent the drive track. During this movement, the cam surfaces 112 and 114 interengage to effect the return stroke of the actuating member 84 and the feeding pawl member 78 connected therewith. The feeding pawl member 78 includes a plurality of rearwardly inclined cam surfaces 118. During the return stroke of the feeding pawl, these surfaces engage the adjacent periphery of the nail shanks and serve to effect a pivotal movement of the feeding pawl against the action of spring 108 out of its normally biased operative position. Toward the end of the return stroke the cam surfaces 118 pass the nails engaged thereby, permitting the spring 108 to return the feeding pawl member back into its operative position.

When the fastener driving element reaches the end of its drive stroke, the nail moved therewith into the feeding position is resiliently held between the rear surface 76 of the fastener driving element and the forward cam surface 112 of the actuating member. In order to prevent upward movement of the nail disposed in the feeding position during the return stroke of the fastener driving element, there is provided a holding pawl member 120. As best shown in FIGS. 6 and 7, the holding pawl is mounted within a slot 122 formed in the side member 24. The lower end of the holding pawl 120 is pivotally mounted within the slot 122, as by a pivot pin 124, as best seen in FIG. 7.

The holding pawl 120 includes a downwardly facing nail head engaging surface 126 disposed in the path of movement of the nail head when the holding pawl member 120 is disposed in an operative limiting position of pivotal movement. In order to yieldingly maintain the holding pawl in such operative position there is provided a leaf spring 128 (FIG. 7) suitably mounted at its upper end to the exterior surface of the side member 24 and having its lower end engaged over the upper end of the slot in engagement with the upper exterior surface of the pawl member 120. The pawl member includes a downwardly inclined cam surface 130 adapted to be engaged by the leading nail head during its movement from the severing position into its feeding position so as to move the feeding pawl out of its operative position against the action of leaf spring 128. As the nail head passes by the holding surface 126, spring 128 serves to resiliently bias the holding pawl back into its operative position where the surface 126 will positively prevent upward movement of the nail during the return stroke of the fastener driving element. As the fastener driving element moves upwardly, the cam surface 114 thereof leaves the cam surface 112. At this position in the return stroke of the fastener driving element, the nail in the feeding position will still be in engagement with the rearward surface 76 of the fastener driving element thus preventing forward movement of the actuating member 84 through its feed stroke under the action of springs 88 and 92. As the fastener driving element continues upwardly through its return stroke the lower end of the nail in the feeding position is moved inwardly into the drive track 14 until the lower end of the fastener driving element clears the nail head, at which time the actuating member 84 commences its feed stroke under the action of springs 88 and 92. This movement serves to effect a forward movement of the leading nail into the severing position as aforesaid. In the normal operation of the device, there will be a nail disposed within the drive track prior to the commencement of the drive stroke of the fastener driving element 16. This nail is driven outwardly of the drive track into a workpiece during the drive stroke of the fastener driving element, the latter including a lower stroking surface which engages the upper surface of the nail head within the drive track.

The piston and cylinder unit preferably embodies a main housing part 130 which is detachably fixedly connected to the side members 24 and 26 at a position which is disposed upwardly and rearwardly from the drive track 14 and fastener driving element 16. Any suitable means may be utilized for effecting the connection of the housing part 130 with the side members 24 and 26. As shown, the housing part 130 is provided with a generally square shaped flange 132 adapted to engage diametrically opposed mounting arms 134 formed on the upper rearward end portion of each of the side members 24 and 26. In addition, a side mounting block 136 is rigidly secured, as by welding or the like, to the exterior surface of each of the members 24 and 26 and extends laterally outwardly therefrom to provide interengagement with the flange 132 at circumferentially spaced positions with respect to the mounting arms 134. The connection is completed by a plurality of bolts 138 extending through the mounting arms 134 and mounting blocks 136 into the flange 132.

In the embodiment shown, the housing part has its interior formed so as to provide a cylindrical drive chamber 140 in its lower end portion, a separate cylindrical return chamber 142 adjacent the upper end portion having a diameter considerably smaller than the diameter of the drive chamber, and an annular reservoir 144 surrounding the return chamber 142. The upper end of the return chamber 142 and reservoir 144 are closed by any suitable means, such as an end closure 146 providing an inlet opening 148 communicating with the reservoir 144 adapted to be connected with a suitable source of air under pressure (not shown).

The piston and cylinder unit 20 also includes a main drive piston 1S0 mounted within the drive chamber 140 for reciprocal movement through successive operative cycles, each including a drive stroke and a return stroke. A return piston 152 is similarly mounted within the return chamber 142 and connected with the drive piston by a connecting rod 154.

Air under pressure communicated to the reservoir 144 is utilized to effect successive operative cycles of the drive piston 150. To this end, appropriate valving is provided to alternately communicate the air pressure from the reservoir 144 to the drive chamber 140 and the return chamber with atmosphere to effect the drive stroke and to communicate with the drive chamber 140 to the atmosphere while the return chainber is communicated with the air under pressure within the reservoir 144 to effect the return stroke. Any conventional valving arrangement known in the art may be utilized including any of the valving arrangements embodied in portable pneumatically actuated fastener driving devices. In the embodiment shown, the housing part 130 is formed with a pair of parallel bores 156 having appropriate passageways extending therefrom in communication with the drive chamber 140, the reservoir 144, and the atmosphere. The third bore 158 is provided which has passageways extending therefrom in communication respectively with the return chamber 142, the reservoir 144 and the atmosphere. The bores 156 are adapted to receive conventional three-way valve assemblies (not shown) adapted to operate in parallel to alternatively communicate the drive chamber 140 to the reservoir 144 and to the atmosphere. The bore 158 is likewise adapted to receive a conventional three-way valve assembly (not shown) operable to communicate the return chamber 142 alternatively to the atmosphere and to the reservoir 144.

As previously indicated, the device 10 is adapted to be embodied in a production machine which may be of a type including automatically operable mechanisms for incrementally feeding successive workpieces into operative position with respect to one or more devices 10. In this regard, it will be understood that the conventional valving utilized is preferably of the type which is remotely controlled and adapted to be integrated in an automatic control circuit of the entire machine. Where the control circuit is pneumatic, the conventional valve assemblies are of the pilot pressure actuated type. As shown in FIG. 1, in order to accommodate pilot pressure operation, the present device 10 may be provided with a manifold block 160 having an opening 162 for connection with a pilot pressure line. As shown in dotted lines in FIG. 1, the opening 162 is connected in parallel with the bores 156 and 158 so as to communicate the same pilot pressure signal to each of the valve assemblies disposed therein. To illustrate an examplary operation, a pilot pressure signal communicated with the opening 162 would serve to actuate both of the conventional valve assemblies within the bores 156 to communicate the drive chamber 140 with the reservoir 144 while simultaneously moving the valve assembly in the bore 158 into a position communicating the return chamber 142 to atmosphere to effect the drive stroke. Conversely, when an atmospheric pilot pressure signal is communicated with the opening 162, the valve assemblies associated with the bores 156 are moved to a position to communicate the drive chamber 140 with the atmosphere while the valve assemblyassociated with the bore 158 is simultaneously moved into a position communicating the return chamber 142 with the reservoir 144 to effect the return stroke.

The linkage 22 for transmitting the movement of the drive piston 150 to the fastener driving element 16 includes a connecting link 164 disposed within cooperating recesses 166 formed within the interior surfaces of the side member 24 and 26. The upper end of the fastener driving element 16 is bifurcated to receive therebetween the lower end of the link 164 which is pivotally connected thereto, as by a pivot pin 168, providing for pivotal movement between the link 164 and fastener driving element 16 about a pivotal axis fixed with respect to the link and the fastener driving element. The opposite end of the link 164 is connected with the drive piston 150 by means of a piston rod member 170. As shown, the piston rod member 170 is preferably of square cross-sectional configuration mounted for reciprocatory movement within a guideway formed by suitable cooperating recesses 172 in the interior surfaces of the side members 24 and 26. The upper surfaces of the recess provides a straight downward and forwardly inclined track against which a roller 174 rides during the reciprocatory movement of the piston rod member 170 within the guideway 172. As shown, the roller 174 is mounted within an appropriate slot extending vertically through the piston rod member at a position spaced from the lower end thereof, the roller 174 being journaled on a shaft 176 extending horizontally through the piston rod member. The lower end of the piston rod member 170 is bifurcated to receive the opposite end of the link 164 therebetween. The link is pivotally connected with the piston rod member, as by a pivot pin 178, providing for pivotal movement between the link 164 and piston rod member 170 about an axis fixed with respect to the link and piston rod member which is parallel with the axis of the pivot pin 168.

The upper end portion of the piston rod member 170 is fixedly connected with the piston 150 for movement therewith. In the embodiment shown, this connection necting element 182 having one end threadedly en gaged within an appropriate matingly threaded bore in the end of the piston rod member 170 and its opposite end formed with a frusto-conical exterior engaged within a corresponding opening within the piston 150. The frustoconical end of the connecting member 182, as shown, has a threaded base therein which receives the adjacent end of the connecting rod 154 of the return piston 152.

The connecting element includes an enlarged annular flange 84 adjacent the piston end thereof and a cylindrical exterior periphery between the flange and the adjacent end of the piston rod member which is of a diameter generally equal to the side dimension of the square piston rod member 170. Mounted over the cylindrical portion of the connecting element 182 in engagement with the annular flange 184 is a rigid washer 186. The flat surface of the washer facing in a direction away from the piston 150 provides a rigid surface fixed with respect to the piston against which a bumper disc 188 of resilient material, such as rubber or the like, is adapted to be compressed. A second rigid washer element 190 disposed in engagement with the opposite surface of the bumper element 188 serves as a compressing means for the bumper disc 188.

In accordance with the principles of the present invention, the connecting element 182, with the washers 186 and 190 mounted thereon and with the bumper elis provided by a prestressed bumper assembly, generally indicated at 180. The assembly includes a conement 188 mounted thereon between the washers, is threadedly engaged within the end of the piston rod member 170 to an extent such that a shoulder means, indicated at 192, formed by the end of the piston rod member extending outwardly from the cylindrical surface of the connecting element 182, retains the compressing washer 190 in spaced relation to the washer 186 sufficient to apply a prestressed compression to the bumper disc 188 which is of the order of 500 psi.

As best shown in FIG. 8, the upwardly and rearwardly facing surfaces of the side members 24 and 26 and mounting blocks 136 are formed with a bore therein of a size to receive the bumper assembly 180, the bore providing a bumper engaging surface 194 rigid with respect to the housing means 12 and facing in a direction toward the piston 150. The bumper engaging surface 194 is disposed in a position to be engaged by the outer surface of the compressing disc 190 of the prestressed bumper assembly when the piston reaches the end of its drive stroke to resiliently arrest the movement of the same. It will be understood that while the prestressed bumper assembly has been shown connected with the piston and engageable with the housing means, the advantages thereof can be equally secured by mounting the assembly on the housing means so as to be engaged by a rigid surface on the piston as it reaches the end of its drive stroke.

OPERATION From the above it is believed that the operation of the device 10 will be apparent. To summarize, however, it will be noted that first the housing means 12 is of particularly rugged and durable construction permitting reliable continuous operation over an extended period of production time. The relationship between the housing part 130 for the piston and cylinder unit 120 and the housing parts 24, 26, 28, 30 and 32 for the fastener driving element 16 and nail feeding mechanism 18 is of particular significance in that this relationship permits the device to be mounted on the frame of the production machine in closely spaced relation to v a similar device 10. As shown in FIG. 2, a second device 10 can either be mounted in nose-to-nose mirrorimage relation, in which case the center line of the drive track 14 which generally coincides with the axis of a nail driven outwardly therefrom is disposed approximately 1% inches from the center line of the drive track of a similar device 10, thus insuring that two devices can be mounted together so as to drive two nails simultaneously on centers as close as 1% inches. In this regard, it will be noted that the tongue 54 of the removable access member 32 is such as to permit removal while the device is disposed in such a relationship with a similar device. Also, as shown in FIG. 2, a similar device may be mounted with respect to the device 10 so that the noses overlap. Here again, access member 32 can be removed while the devices are mounted in such relationship and the devices are capable of simultaneously firing two nails with their axes spaced as close as 1% inches apart.

The position of the power unit upwardly and rearwardly of the drive track 14 and fastener driving element 16 is not only desirable for the reasons indicated above, but permits the utilization of a linkage 22 which provides a highly desirable force and velocity transmission of the movement of the drive piston 150 to the fastener driving element 16. It can be seen that because of the angle of the link 164 changes in relation to the piston rod member 170 and fastener driving element 16 during both the drive stroke and the return stroke, the output force and speed of the fastener drive element 16 is varied with respect to the input force and speed of the drive piston 150. The variance is such as to provide for a maximum velocity and minimum force of the fastener driving element at the beginning of the drive stroke and a minimum velocity and maximum force at the end of the drive stroke, the velocity decreasing from maximum to minimum and the force increasing from minimum to maximum during the drive stroke.

The size of the power unit 20 is chosen to provide more than a minimum required to effect the driving action. In this regard, the provision of a prestressed bumper assembly 180 is of particular significance. By prestressing the bumper assembly, the latter is capable of arresting a greater force with considerably less deflection. Thus, with this arrangement the moving parts driven by the more-than-adequate energy provided by the unit 20 are resiliently resisted at the end of the drive 1 stroke in a manner insuring an accurate terminating position of the drive stroke so that the device will consistently drive the nails into the workpiece to the desired extent under varying conditions.

The nail feeding mechanism 18 provides a highly effi- Y cient handling of successive nails. The arrangement permits the utilization of a nail package of maximum capacity; namely, a large coil formation which can be separately supported in any desired position on the production machine frame remote from the device 10. The roller arrangement 62 insures proper feeding of the leading portion of the nail package into the nail feeding mechanism 18 from any direction. The nail feeding mechanism 18 is operable to handle only a limited number of nails in the leading portion of the package. The feed path of the leading portion of the nail package is a desirable straight horizontal feed path which is spaced above the lower end of the drive track. The

ratchet means embodied in the feeding mechanism 18 for feeding the leading portion of the fastener package along the straight feed path functions to feed successive leading nails into a severing position during each operative cycle. The nail in the severing position is stripped from the package during the drive stroke by engagement of the surface 116 with its head and is subsequently moved downwardly into a feeding position where it is retained through the operation of the spring pressed pawl member 120. The movement of the feeding pawl 78 in the preferred embodiment shown is positively moved through its return stroke through the interengagement of cam surface 1 14 on the fastener driving element and cam surface 112 on the actuating member 84. Simultaneously with the movement of the leading nail from the severing position into the feeding position during the drive stroke of the fastener driving element 16, the nail within the drive track 14 is driven outwardly therefrom into the workpiece. During the return stroke the actuating member 84 serves to move the nail in the feeding position forwardly into the drive track 14, while the feeding pawl 78 simultaneously effects movement of the leading nail of the package into the severing position.

It thus will be seen that the objects of this invention have been fully and efi'ectively accomplished. It will be realized, however, that the foregoing preferred specific embodiment has been shown and described for the purpose of illustrating the functional and structural principles of this invention and is subject to change without departure from such principles. Therefore, this invention includes all modifications encompassed within the spirit and scope of the following claims.

I claim:

1. A fastener driving device comprising a housing structure, means defining a vertically extending drive track in said housing structure, a fastener driving element mounted in said drive track for vertical sliding movement through successive cycles including a downward drive stroke and an upward return stroke, means for receiving a fastener package of the type including a multiplicity of headed nails disposed with their shanks in generally parallel relation and interconnected in series by means permitting successive leading nails to be severed from the package and for feeding successive leading nails into said drive track to be driven outwardly thereof into a workpiece by said fastener driving element during the drive stroke thereof, means defining a cylindrical drive chamber in said housing structure, said cylindrical chamber being disposed in fixed upwardly and rearwardly spaced relation to said drive track, a drive piston slidably mounted within said cylindrical chamber for reciprocating movement through successive cycles including a drive stroke and a return stroke, means operatively connecting said piston with said fastener driving element for effecting movement of said fastener driving element through its drive stroke in response to the movement of said piston through its drive stroke, said housing structure including a vertically extending portion disposed forwardly and on one side of said drive track and extending thereabove, and an access member disposable in an operative position with respect to said vertically extending portion, said means defining said drive track including cooperating interior surfaces formed in said vertically extending portion and said access member when the latter is in said operative position, said vertically extending portion having forwardly facing exterior surface means of a shape permitting said device to be positioned with respect to a similar device with the forwardly facing exterior surface means thereof in substantially abutting relation so that both of said devices are capable of simultaneously driving parallel nails into a workpiece with a spacing of approximately 1% inches between the axes of said nails, said vertically extending portion having laterally facing exterior surface means adjacent said one side permitting said device to be positioned with respect to a similar device with the laterally facing exterior surface means thereof disposed in substantially abutting relation so that both of said devices are capable of simultaneously driving parallel nails into a work piece with a spacing of approximately 1% inches between the axes of said nails, said access member comprising a movable elongated member having a flange extending laterally and rearwardly from the forward portion thereof, said vertically extending portion having recess means formed in the exterior thereof for receiving said flange in response to a lateral and rearward movement of said access member within a space rearwardly of a vertical plane touching said forwardly facing surface means.

2. A fastener driving device as defined in claim 1 wherein said housing structure includes a cylindrical member disposed with its axis extending downwardly and forwardly, said means defining said cylindrical chamber comprising a cylindrical surface within said cylindrical member having an axis concentric with the axis of said cylindrical member, a pair of side members fixed together in side-by-side relation and fixedly connected at their upper rearward portions with the downwardly and forwardly extending end of said cylindrical member, the forward portion of said side members constituting the vertically extending portion of said housing structure, the side member corresponding with said one side extending downwardly below the other of said side members.

3. A fastener driving device as defined in claim 2 wherein said means operatively connecting said piston with said fastener driving element comprises a piston rod connected with said piston and extending downwardly and forwardly therefrom and a connecting link pivotally connected at one end with the forward end portion of said piston rod and at its opposite end with the upper end portion of said fastener driving element, said side members having cooperating interior surfaces providing a guide track for guidingly receiving said piston rod and a communicating recess for receiving said link.

4. A fastener driving device as defined in claim 3 wherein said piston and said housing structure each have a portion fixed with respect thereto, said fixed portions having opposed surface means facing toward one another spaced apart a predetermined distance when said piston is disposed in a position corresponding to the completion of said drivestroke, a compressible member of resilient material having first surface means facing in a direction opposed to the surface means of one of said fixed portions and disposed in engagement therewith and second surface means facing in the opposite direction, compressing means for engaging the surface means of the other of said fixed portions in response to the completion of the drive stroke of said piston and means mounting said compressing means with respect to said one fixed portion in a normal position of engagement with the second surface means of said compressible member in which the latter is compressed between said compressing means and said one fixed portion and for movement from said normal position toward said one fixed portion to further compress said compressible member therebetween in response to the interengagement of the surface means of said compressing means and said other fixed portion at the completion of the drive stroke of said piston.

5. A fastener driving device as defined in claim 4 wherein said nail package receiving and feeding means comprises means for supporting the leading portion of said fastener package beneath the heads thereof for forward movement along a feed path in which the leading nail is moved into a severing position disposed rearwardly adjacent said drive track, said fastener driving element having a downwardly facing lower surface for engaging the head of a nail disposed in said drive track and driving the engaged nail outwardly of the drive track into a workpiece during the drive stroke of said fastener driving element, a rearwardly facing surface extending upwardly from said lower surface for engaging the leading surface of a nail disposed in said severing position and a downwardly facing upper surface extending rearwardly from the upper end of said rearwardly facing surface in vertically spaced relation to said lower surface for engaging the head of a nail disposed in said severing position and moving the engaged nail from said severing position downwardly into a feed position during the drive stroke of said fastener driving element, means engageable with nail shanks in the leading portion of said package for advancing successive leading nails of the package into said severing position to be moved therefrom by said fastener driving element during the drive stroke thereof into said feed position, and means engageable with the nail in said feed position for moving the latter forwardly into a drive position within said drive track so as to be driven outwardly thereof into a workpiece by said fastener driving element during the drive stroke.

6. A fastener driving device as defined in claim 5 wherein said means for supporting the leading portion of the fastener package beneath the heads thereof comprises an elongated upwardly facing shoulder formed by a groove in the interior surface of said one side member below the other side member, said housing structure including a second access member mounted for movement between an operative position in sideby-side relation to said one side member and below and rearwardly of said other side member and said firstmentioned access member respectively and an access position permitting lateral access to said elongated shoulder, and means for releasably retaining said second access member in its operative position and for retaining said first-mentioned access member in its operative position when said second access member is disposed in its operative position.

7. A fastener driving device as defined in claim 6 wherein said means for supporting the leading portion of the fastener package beneath the heads thereof includes a pair of rollers and means mounting said rollers for rotational movement about laterally spaced vertically extending axes, said rollers including peripheral surfaces for engaging the nail shanks and upwardly facing annular surfaces aligned with said shoulder for engaging beneath the nail heads.

8. A fastener driving device as defined in claim 7 wherein said roller mounting means includes a mounting arm assembly for each roller, said mounting arm assemblies being carried by said one side member and said second access member respectively and providing for resiliently biased movement of said rollers toward one another.

9. A fastener driving device as defined in claim 8 wherein said means engageable with the nail in said feed position comprises a nail feeding member mounted in said housing structure for movement through successive cycles including a feed stroke and a return stroke, said nail feeding member being biased to move through said feed stroke and having a cam surface engageable by said fastener driving element during the drive stroke thereof for effecting the return stroke of said nail feeding member, said means for advancing successive leading nails into said severing position comprising a feeding pawl and a holding pawl each having forwardly facing nail shank engaging surface means and inclined rearwardly facing cam surface means, means mounting said feeding pawl on said nail feeding member for movement through feed and return strokes with said nail feeding member and for biased movement with respect to said nail feeding member into an operative position within said feed path 'so that the nail engaging surface means thereof is operable to engage a nail shank and effect movement of the leading nail into said severing position during the feed stroke thereof, and means mounting said holding pawl on said one side member for biased movement into an operative position within said feed path so that the cam surface means thereof is operable to be engaged by a nail shank advanced during the feeding stroke of said feeding pawl to move said feeding pawl out of and back into said operative position and the nail shank engaging surface means of said holding pawl is operable to engage the nail shank and prevent rearward movement of the leading portion of the fastener package during the return stroke of said feeding pawl in which the cam surface means thereof is operable to engage a nail shank and move said feeding pawl out of and back into said operative position.

10. A fastener driving device as defined in claim 9 ineluding holding pawl means for engaging the upper surface of a nail head in response to the movement of a nail into said feed position for preventing upward movement of said nail with said fastener driving element out of said feed position during the return stroke of said fastener driving element.

11. A fastener driving device comprising a housing structure, means defining a vertically extending drive track in said housing structure, a fastener driving element mounted in said drive track for vertical sliding movement through successive cycles including a downward drive stroke and an upward return stroke, means for feeding successive fasteners forwardly into said drive track to be driven outwardly thereof into a workpiece by said fastener driving element during the drive stroke thereof, means defining a cylindrical drive chamber in said housing structure, said cylindrical chamber being disposed in upwardly and rearwardly spaced relation to said drive track and having its axis extending upwardly and rearwardly from a point of intersection with the axis of said drive track which defines an obtuse angle therebetween, a drive piston slidably mounted within said cylindrical chamber for reciprocating movement through successive cycles including a drive stroke and a return stroke, and an elongated link having one end pivotally connected with said pis ton about an axis fixed with respect to said link and said piston and the other end pivotally connected with said fastener driving element aobut a parallel axis fixed with respect to said link and said fastener driving element for effecting movement of said fastener driving element through its drive stroke in response to the movement of said piston through its drive stroke at a speed which decreases and with a force which increases with respect to the speed and force of said piston drive stroke as the fastener driving element approaches the completion of the drive stroke, said piston and said housing structure each having a portion fixed with respect thereto, said fixed portions having opposed surface means facing toward one another spaced apart a predetermined distance when said piston is disposed in a position corresponding to the completion of said drive stroke, a compressible member of resilient material having first surface means facing in a direction opposed to the surface means of one of said fixed portions and disposed in engagement therewith and second surface means facing in the opposite direction, compressing means for engaging the surface means of the other of said fixed portions in response to the completion of the drive stroke of said piston and means mounting said compressing means with respect to said one fixed portion in a normal position of engagement with the second surface means of said compressible member in which the latter is compressed between said compressing means and said one fixed portion and for movement from said normal position toward said one fixed portion to further compress said compressible member therebetween in response to the interengagement of the surface means of said compressing means and said other fixed portion at the completion of the drive stroke of said piston.

12. A fastener driving device as defined in claim 11 wherein said fastener feeding means is adapted to feed a fastener package of the type including a multiplicity of headed nails disposed with their shanks in generally parallel relation and interconnected in series by means permitting successive leading nails to be severed from the package and comprises means for supporting the leading portion of said fastener package beneath the heads thereof for forward movement along a feed path in which the leading nail is moved into a severing position disposed rearwardly adjacent said drive track, said fastener driving element having a downwardly facing lower surface for engaging the head of a nail disposed in said drive track and driving the engaged nail outwardly of the drive track into a workpiece during the drive stroke of said fastener driving element, a rearwardly facing surface extending upwardly from said lower surface for engaging the leading surface of a nail disposed in said severing position and a downwardly facing upper surface extending rearwardly from the upper end of said rearwardly facing surface in vertically spaced relation to said lower surface for engaging the head of a nail disposed in said severing position and moving the engaged nail from said severing position downwardly into a feed position during the drive stroke of said fastener driving element, means engageable with nail shanks in the leading portion of said package for advancing successive leading nails of the package into said severing position to be moved therefrom by said fastener driving element during the drive stroke thereof into said feed position, and means engageable with the nail in said feed position for moving the latter forwardly into a drive position within said drive track so as to be driven outwardly thereof into a workpiece by said fastener driving element during the drive stroke.

13. A fastener driving device as defined in claim 12 wherein said means engageable with the nail in said feed position comprises a nail feeding member mounted in said housing structure for movement through successive cycles including a feed stroke and a return stroke, said nail feeding member being biased to move through said feed stroke and having a cam surface engageable by said fastener driving element during the drive stroke thereof for effecting the return stroke of said nail feeding member, said means for advancing successive leading nails into said severing position comprising a feeding pawl and a holding pawl each having forwardly facing nail shank engaging surface means and inclined rearwardly facing cam surface means, means mounting said feeding pawl on said nail feeding member for movement through feed and return strokes with said nail feeding member and for biased movement with respect to said nail feeding member into an operative position within said feed path so that the nail engaging surface means thereof is operable to engage a nail shank and effect movement of the leading nail into said severing position during the feed stroke thereof, and means mounting said holding pawl on said housing structure for biased movement into an operative position within said feed path so that the cam surface means thereof is operable to be engaged by a nail shank advanced during the feeding stroke of said feeding pawl to move said feeding pawl out of and back into said operative position and the nail shank engaging surface means of said holding pawl is operable to engage the nail shank and prevent rearward movement of the leading portion of the fastener package during the return stroke of said feeding pawl in which the cam surface means thereof is operable to engage a nail shank and move said feeding pawl out of and back into said operative position.

14. A fastener driving device as defined in claim 13 including holding pawl means for engaging the upper surface of a nail head in response to the movement of a nail into said feed position for preventing upward movement of said nail with said fastener driving element out of said feed position during the return stroke of said fastener driving element.

15. A fastener driving device as defined in claim 11 wherein said link is connected with said piston by means including an elongated piston rod member fixedly connected at one end with said piston and pivoted to said link at the other end, said housing structure including means defining a guidway for receiving said piston rod member including a straight elongated guide surface facing downwardly and rearwardly and roller means joumaled on said piston rod member in a position to roll on said guide surface.

16. A fastener driving device comprising a housing structure, means defining an elongated vertically ex- -tending drive track in said housing structure, means for receiving a fastener package of the type including a multiplicity of headed nails disposed with their shanks in generally parallel relation and interconnected in series by means permitting successive leading nails to be severed from the package and for supporting a leading portion of said fastener package beneath the heads thereof for forward movement along a feed path in which the leading nail is moved into a severing position disposed rearwardly adjacent said drive track, an elongated fastener driving element slidably mounted in said drive track for downward movement through a drive stroke and for upward movement through a return stroke, said fastener driving element having a downwardly facing lower surface for engaging the head of a nail disposed in said drive track and driving the engaged nail outwardly of the drive track into a workpiece during the drive stroke of said fastener driving element, a rearwardly facing surface extending upwardly from said lower surface for. engaging the leading surface of a nail disposed in said severing position, and a downwardly facing upper surface extending rearwardly from the upper end of said rearwardly facing surface in vertically spaced relation to said lower surface for engaging the head of a nail disposed in said severing position and moving the engaged nail from said severing position downwardly into a feed position during the drive stroke of said fastener driving element, power operated means carried by said housing structure for effecting the drive stroke and return stroke of said fastener driving element, nail package advancing means engageable with successive nail shanks in the leading portion of said package and movable through successive feed strokes for advancing successive leading nails of the package into said severing position to be moved therefrom by said fastener driving element during the drive stroke thereof into said feed position in severed relation from the package, and severed nail feeding means engageable with successive severed nails in said feed position and movable through successive feed strokes simultaneously with the feed strokes of said nail package advancing means for moving successive severed nails forwardly into a drive position within said drive track so as to be driven outwardly thereof into a workpiece by said fastener driving element during the drive stroke thereof.

17. A fastener driving device comprising a housing structure, means defining an elongated vertically extending drive track in said housing structure, means for receiving a fastener package of the type including a multiplicity of headed nails disposed with their shanks in generally parallel relation and interconnected in series by means permitting successive leading nails to be severed from the package and for supporting a leading portion of said fastener package beneath the heads thereof for forward movement along a feed path in which the leading nail is moved into a severing position disposed rearwardly adjacent said drive track, an elongated fastener driving element slidably mounted in said drive track for downward movement through a drive stroke and for upward movement through a return stroke, said fastener driving element having a downwardly facing lower surface for engaging the head of a nail disposed in said drive track and driving the engaged nail outwardly of the drive track into a workpiece during the drive stroke of said fastener driving element, a rearwardly facing surface extending upwardly from said lower surface for engaging the leading surface of a nail disposed in said severing position, and a downwardly facing upper surface extending rearwardly from the upper end of said rearwardly facing surface in vertically spaced relation to said lower surface for engaging the head of a nail disposed in said severing position and moving the engaged nail from said severing position downwardly into a feed position during the drive stroke of said fastener driving element, power operated means carried by said housing structure for effecting the drive stroke and return stroke of said fastener driving element, means engageable with nail shanks in the leading portion of said package for advancing successive leading nails of the package into said severing position to be moved therefrom by said fastener driving element during the drive stroke thereof into said feed position, and means engageable with the nail in said feed position for moving the latter forwardly into a drive position within said drive track so as to be driven outwardly thereof into a workpiece by said fastener driving element during the drive stroke thereof, said means engageable with the nail in said feed position comprising a nail feeding member mounted in said housing structure for movement through successive cycles including a feed stroke and a return stroke, said nail feeding member being biased to move through said feed stroke and having a cam surface engageable by said fastener driving element during the drive stroke thereof for effecting the return stroke of said nail feeding member, said means for advancing successive leading nails into said severing position comprising a feeding pawl and a holding pawl each having forwardly facing nail shank engaging surface means and inclined rearwardly facing cam surface means, means mounting said feeding pawl on said nail feeding member for movement through feed and return strokes with said nail feeding member and for biased movement with respect to said nail feeding member into an operative position within said feed path so that the nail engaging surface means thereof is operable to engage a nail shank and effect movement of the leading nail into said severing position during the feed stroke thereof, and means mounting said holding pawl on said housing structure for biased movement into an operative position within said feed path so that the cam surface means thereof is operative to be engaged by a nail shank advanced during the feed stroke of said feeding pawl so as to move said holding pawl out of and back into said operative position and the nail shank engaging surface means of said holding pawl is operable to engage the nail shank and prevent rearward movement of the leading portion of the fastener package during the return stroke of said feeding pawl and in which the cam surface means thereof is operable to engage a nail shank and move said feeding pawl out of and back into said operative position.

18. A fastener driving device asdefined in claim 17 including holding pawl means for engaging the upper surface of a nail head in response to the movement of a nail into said feed position for preventing upward movement of said nail with said fastener driving element out of said feed position during the return stroke of said fastener driving element,

19. A fastener driving device as defined in claim 18 wherein said means for supporting the leading portion of the fastener package beneath the heads thereof includes a pair of rollers and means mounting said rollers for rotational movement about laterally spaced vertically extending axes, said rollers including peripheral surfaces for engaging the nail shanks and upwardly facing annular surfaces for engaging beneath the nail heads.

20. Afastener driving device as defined in claim 19 wherein said roller mounting means includes a mounting arm assembly for each roller, said mounting arm assemblies having means for resiliently biasing said rollers for movement toward one another.

21. A fastener driving device a housingstructure, means defining an elongated vertically extending drive track in said housing structure, means for receiving a fastener package of the type including a multiplicity of headed nails disposed with their shanks in generally parallel relation and interconnected in series by means permitting successive leading nails to be severed from the package and for supporting a leading portion of said fastener package beneath the heads thereof for forward movement along a feed path in which the leading nail is moved into a severing position disposed rearwardly adjacent said drive track, an elongated fastener driving element slidably mounted in said drive track for downward movement through a drive stroke and for upward movement through a return stroke, said fastener driving element having a downwardly facing lower surface for engaging the head of a nail disposed in said drive track and driving the engaged nail outwardly of the drive track into a workpiece during the drive stroke of said fastener driving element, a rearwardly facing surface extending upwardly from said lower surface for engaging the leading surface of a nail disposed in said severing position, and a downwardly facing upper surface extending rearwardly from the upper end of said rearwardly facing surface in vertically spaced relation to said lower surface for engaging the head of a nail disposed in said severing position and moving the engaged nail from said severing position downwardly into a feed position during the drive stroke of said fastener driving element, power operated means carried by said housing structure for effecting the drive stroke and return stroke of said fastener driving element, means engageable with nail shanks in the leading portion of said package for advancing successive leading nails of the package into said severing position to be moved therefrom by said fastener driving element during the drive stroke thereof into said feed position, and means engageable with the nail in said feed position for moving the latter forwardly into a drive position within said drive track so as to be driven outwardly thereof into a workpiece by said fastener driving element during the drive stroke thereof, and holding pawl means separate from said nail moving means engageable with the nail in said feed position for engaging the upper surface of a nail head in response to the movement of a nail into said feed position for preventing upward movement of said nail with said fastener driving element out of said feed position during the return stroke of said fastener driving element.

22. A fastener driving device comprising a housing structure, means defining an elongated vertically extending drive track in said housing structure, means for receiving a fastener package of the type including a multiplicity of headed nails disposed with their shanks in generally parallel relation and interconnected in series by means permitting successive leading nails to be severed from the package and for supporting a leading portion of said fastener package beneath the heads thereof for forward movement along a feed path in which the leading nail is moved into a severing position disposed rearwardly adjacent said drive track, an elongated fastener driving element slidably mounted in said drive track for downward movement through a drive stroke and for upward movement through a return stroke, said fastener driving element having a downwardly facing lower surface for engaging the head of a nail disposed in said drive track and driving the engaged nail outwardly of the drive track into a workpiece during the drive stroke of said fastener driving element, a rearwardly facing surface extending upwardly from said lower surface for engaging the leading surface of a nail disposed in said severing position, and a downwardly facing upper surface extending rearwardly from the upper end of said rearwardly facing surface in vertically spaced relation to said lower surface for engaging the head of a nail disposed in said severing position and moving the engaged nail from said severing position downwardly into a feed position during the drive stroke of said fastener driving element, power operated means carried by said housing structure for effecting the drive stroke and return stroke of said fastener driving element, means engageable with nail shanks in the leading portion of said package for advancing successive leading nails of the package into said severing position to be moved therefrom by said fastener driving element during the drive stroke thereof into said feed position, and means engageable with the nail in said feed position for moving the latter forwardly into a drive position within said drive track so as to be driven outwardly thereof into a workpiece by said fastener driving element during the drive stroke thereof, said means for supporting the leading portion of the fastener package beneath the heads thereof including a pair of rollers and means mounting said rollers for rotational movement about laterally spaced vertically extending axes, said rollers including peripheral surfaces for engaging the nail shanks and upwardly facing annular surfaces for engaging beneath the nail heads.

23. A fastener driving device comprising a housing structure, means defining an elongated vertically extending drive track in said housing structure, means for receiving a fastener package of the type including a multiplicity of headed nails disposed with their shanks in generally parallel relation and interconnected in series by means permitting successive leading nails to be severed from the package and for supporting a leading portion of said fastener package beneath the heads thereof for forward movement along a feed path in which the leading nail is movedinto a severing position disposed rearwardly adjacent said drive track, an elongated fastener driving element slidably mounted in said drive track for downward movement through a drive stroke and for upward movement through a return stroke, said fastener driving element having a downwardly facing lower surface for engaging the head of a nail disposed in said drive track and driving the engaged nail outwardly of the drive track into a workpiece during the drive stroke of said fastener driving element, a rearwardly facing surface extending upwardly from said lower surface for engaging the leading surface of a nail-disposed in said severing position, and a downwardly facing upper surface extending rearwardly from the upper end of said rearwardly facing surface in vertically spaced relation to said lower surface for engaging the head of a nail disposed in said severing position and moving the engaged nail from said severing position downwardly into a feed position during the drive stroke of said fastener driving element, power operated means carried by said housing structure for effecting the drive stroke and return stroke of said fastener driving element, means engageable with nail shanks in the leading portion of said package for advancing successive leading nails of the package into said severing position to be moved therefrom by said fastener driving element during the drive stroke thereof into said feed position, and means engageable with the nail in said feed position for moving the latter forwardly into a drive position within said drive track so as to be driven outwardly thereof into a workpiece by said fastener driving element during the drive stroke thereof, said power operated means including means defining a cylindrical chamber and a piston mounted within said chamber for movement through successive operative cycles each including a drive stroke and a return stroke, said piston and said housing structure each have a portion fixed with respect thereto, said fixed portions having opposed surface means facing toward one another spaced apart a predetermined distance when said piston is disposed in a position corresponding to the completion of said drive stroke, a compressible member of resilient material having first surface means facing in a direction opposed to the surface means of one of said fixed portions and disposed in engagement therewith and second surface means facing in the opposite direction, compressing means for engaging the surface means of the other of said fixed portions in response to the completion of the drive stroke of said piston and means mounting said compressing means with respect to said one fixed portion in a normal position of engagement with the second surface means of said compressible member in which the latter is compressed between said compressing means and said one fixed portion and for movement from said normal position toward said one fixed portion to further compress said compressible member therebetween in response to the interengagement of the surface means of said compressing means and said other fixed portion at the completion of the drive stroke of said piston.

24. A fastener driving device comprising a housing structure, means defining an elongated vertically extending drive track in said housing structure, means for receiving a fastener package of the type including a multiplicity of headed nails disposed with their shanks in generally parallel relation and interconnected in series by means permitting successive leading nails to be 'severed from the package and for supporting a leading portion of said fastener package beneath the heads thereof for forward movement along a feed path in which the leading nail is moved into a severing position disposed rearwardly adjacent said drive track, an elongated fastener driving element slidably mounted in said drive track for downward movement through a drive stroke and for upward movement through a return stroke, said fastener driving element having a downwardly facing lower surface for engaging the head of a nail disposed in said drive track and driving the engaged nail outwardly of the drive track into a workpiece during the drive stroke of said fastener driving element, a rearwardly facing surface extending upwardly from said lower surface for engaging the leading surface of a nail disposed in said severing position, and a downwardly facing upper surface extending rearwardly from the upper end of said rearwardly facing surface in vertically spaced relation to said lower surface for engaging the head of a nail disposed in said severing position and moving the engaged nail from said severing position downwardly into a feed position during the drive stroke of said fastener driving element, power operated means carried by said housing structure for effecting the drive stroke and return stroke of said fastener driving element, means engageable with nail shanks in the leading portion of said package for advancing successive leading nails of the package into said severing position to be moved therefrom by said fastener driving element during the drive stroke thereof into said feed position, and means engageable with the nail in said feed position for moving the latter forwardly into a drive position within said drive track so as to be driven outwardly thereof into a workpiece by said fastener driving element during the drive stroke thereof, said housing structure including a pair of side members fixed together in side-by-side relation, one of said side members extending downwardly below the other of said side members, an access member mounted for movement into and out of an operative position disposed in cooperating side-by-side relation to said one side member below the other side member, said means defining said drive track including cooperating interior surfaces formed in said pair of side members and said access member, the portion of said interior surfaces formed in said access member being such that when said access member is disposed out of said operative position lateral access is provided to the portion of the drive track into which successive fasteners are fed by said fastener feeding means, said means for supporting the leading portion of the fastener package beneath the heads thereof comprising an elongated upwardly facing shoulder formed by a groove in the interior surface of said one side member below the other side member, said housing structure further including a second access member mounted for movement between an operative position in side-by-side relation to said one side member and below and rearwardly of said other side member and said first-mentioned access member respectively and an access position permitting lateral access to said elongated shoulder, and means for releasably retaining said second access member in its operative position and for retaining said first-mentioned access member in its operative position when said second access member is disposed in its operative position.

25. A fastener driving device comprising a housing structure, means defining a cylindrical drive chamber in said housing structure, a drive piston slidably mounted within said drive chamber for reciprocating movement through successive operative cycles each including a drive stroke and a return stroke, means defining a drive track within said housing structure for receiving successive fasteners therein, a fastener driving element slidably mounted in said drive track and operatively connected with said drive piston for movement through a drive stroke to drive a fastener within said drive track outwardly thereof into a workpiece in response to the movement of said piston through its drive stroke and through return stroke in response to the movement of said piston through its return stroke, said piston and said housing structure each having a portion fixed with respect thereto, said portions having opposed surface means facing toward one another spaced apart a predetermined distance when said piston is disposed in a portion corresponding to the completion of said drive stroke, a compressible member of resilient material having first surface means facing in a direction opposed to the surface means of one of said portions and disposed in engagement therewith and second surface means facing in the opposite direction, compressing means for engaging the surface means of the other of said portions in response to the completion of the drive stroke of said piston, and means mounting said compressing means with respect to said one portion in a normal position of engagement with the second surface means of said compressible member in which the latter is compressed between said compressing means and said one portion and for movement from said normal position toward said one portion to further compress said compressible member therebetween in response to the interengagement of the surface means of said compressing means and said other portion at the completion of the drive stroke of said piston.

26. A fastener driving device as defined in claim 25 wherein said one portion is fixed with respect to said piston. 

1. A fastener driving device comprising a housing structure, means defining a vertically extending drive track in said housing structure, a fastener driving element mounted in said drive track for vertical sliding movement through successive cycles including a downward drive stroke and an upward return stroke, means for receiving a fastener package of the type including a multiplicity of headed nails disposed with their shanks in generally parallel relation and interconnected in series by means permitting successive leading nails to be severed from the package and for feeding successive leading nails into said drive track to be driven outwardly thereof into a workpiece by said fastener driving element during the drive stroke thereof, means defining a cylindrical drive chamber in said housing structure, said cylindrical chamber being disposed in fixed upwardly and rearwardly spaced relation to said drive track, a drive piston slidably mounted within said cylindrical chamber for reciprocating movement through successive cycles including a drive stroke and a return stroke, means operatively connecting said piston with said fastener driving element for effecting movement of said fastener driving element through its drive stroke in response to the movement of said piston through its drive stroke, said housing structure including a vertically extending portion disposed forwardly and on one side of said drive track and extending thereabove, and an access member disposable in an operative position with respect to said vertically extending portion, said means defining said drive track including cooperating interior surfaces formed in said vertically extending portion and said access member when the latter is in said operative position, said vertically extending portion having forwardly facing exterior surface means of a shape permitting said device to be positioned with respect to a similar device with the forwardly facing exterior surface means thereof in substantially abutting relation so that both of said devices are capable of simultaneously driving parallel nails into a workpiece with a spacing of approximately 1 1/4 inches between the axes of said nails, said vertically extending portion having laterally facing exterior surface means adjacent said one side permitting said device to be positioned with respect to a similar device with the laterally facing exterior surface means thereof disposed in substantially abuttIng relation so that both of said devices are capable of simultaneously driving parallel nails into a workpiece with a spacing of approximately 1 1/4 inches between the axes of said nails, said access member comprising a movable elongated member having a flange extending laterally and rearwardly from the forward portion thereof, said vertically extending portion having recess means formed in the exterior thereof for receiving said flange in response to a lateral and rearward movement of said access member within a space rearwardly of a vertical plane touching said forwardly facing surface means.
 2. A fastener driving device as defined in claim 1 wherein said housing structure includes a cylindrical member disposed with its axis extending downwardly and forwardly, said means defining said cylindrical chamber comprising a cylindrical surface within said cylindrical member having an axis concentric with the axis of said cylindrical member, a pair of side members fixed together in side-by-side relation and fixedly connected at their upper rearward portions with the downwardly and forwardly extending end of said cylindrical member, the forward portion of said side members constituting the vertically extending portion of said housing structure, the side member corresponding with said one side extending downwardly below the other of said side members.
 3. A fastener driving device as defined in claim 2 wherein said means operatively connecting said piston with said fastener driving element comprises a piston rod connected with said piston and extending downwardly and forwardly therefrom and a connecting link pivotally connected at one end with the forward end portion of said piston rod and at its opposite end with the upper end portion of said fastener driving element, said side members having cooperating interior surfaces providing a guide track for guidingly receiving said piston rod and a communicating recess for receiving said link.
 4. A fastener driving device as defined in claim 3 wherein said piston and said housing structure each have a portion fixed with respect thereto, said fixed portions having opposed surface means facing toward one another spaced apart a predetermined distance when said piston is disposed in a position corresponding to the completion of said drive stroke, a compressible member of resilient material having first surface means facing in a direction opposed to the surface means of one of said fixed portions and disposed in engagement therewith and second surface means facing in the opposite direction, compressing means for engaging the surface means of the other of said fixed portions in response to the completion of the drive stroke of said piston and means mounting said compressing means with respect to said one fixed portion in a normal position of engagement with the second surface means of said compressible member in which the latter is compressed between said compressing means and said one fixed portion and for movement from said normal position toward said one fixed portion to further compress said compressible member therebetween in response to the interengagement of the surface means of said compressing means and said other fixed portion at the completion of the drive stroke of said piston.
 5. A fastener driving device as defined in claim 4 wherein said nail package receiving and feeding means comprises means for supporting the leading portion of said fastener package beneath the heads thereof for forward movement along a feed path in which the leading nail is moved into a severing position disposed rearwardly adjacent said drive track, said fastener driving element having a downwardly facing lower surface for engaging the head of a nail disposed in said drive track and driving the engaged nail outwardly of the drive track into a workpiece during the drive stroke of said fastener driving element, a rearwardly facing surface extending upwardly from said lower surface for engaging the leading surface of a nail disposed in said Severing position and a downwardly facing upper surface extending rearwardly from the upper end of said rearwardly facing surface in vertically spaced relation to said lower surface for engaging the head of a nail disposed in said severing position and moving the engaged nail from said severing position downwardly into a feed position during the drive stroke of said fastener driving element, means engageable with nail shanks in the leading portion of said package for advancing successive leading nails of the package into said severing position to be moved therefrom by said fastener driving element during the drive stroke thereof into said feed position, and means engageable with the nail in said feed position for moving the latter forwardly into a drive position within said drive track so as to be driven outwardly thereof into a workpiece by said fastener driving element during the drive stroke.
 6. A fastener driving device as defined in claim 5 wherein said means for supporting the leading portion of the fastener package beneath the heads thereof comprises an elongated upwardly facing shoulder formed by a groove in the interior surface of said one side member below the other side member, said housing structure including a second access member mounted for movement between an operative position in side-by-side relation to said one side member and below and rearwardly of said other side member and said first-mentioned access member respectively and an access position permitting lateral access to said elongated shoulder, and means for releasably retaining said second access member in its operative position and for retaining said first-mentioned access member in its operative position when said second access member is disposed in its operative position.
 7. A fastener driving device as defined in claim 6 wherein said means for supporting the leading portion of the fastener package beneath the heads thereof includes a pair of rollers and means mounting said rollers for rotational movement about laterally spaced vertically extending axes, said rollers including peripheral surfaces for engaging the nail shanks and upwardly facing annular surfaces aligned with said shoulder for engaging beneath the nail heads.
 8. A fastener driving device as defined in claim 7 wherein said roller mounting means includes a mounting arm assembly for each roller, said mounting arm assemblies being carried by said one side member and said second access member respectively and providing for resiliently biased movement of said rollers toward one another.
 9. A fastener driving device as defined in claim 8 wherein said means engageable with the nail in said feed position comprises a nail feeding member mounted in said housing structure for movement through successive cycles including a feed stroke and a return stroke, said nail feeding member being biased to move through said feed stroke and having a cam surface engageable by said fastener driving element during the drive stroke thereof for effecting the return stroke of said nail feeding member, said means for advancing successive leading nails into said severing position comprising a feeding pawl and a holding pawl each having forwardly facing nail shank engaging surface means and inclined rearwardly facing cam surface means, means mounting said feeding pawl on said nail feeding member for movement through feed and return strokes with said nail feeding member and for biased movement with respect to said nail feeding member into an operative position within said feed path so that the nail engaging surface means thereof is operable to engage a nail shank and effect movement of the leading nail into said severing position during the feed stroke thereof, and means mounting said holding pawl on said one side member for biased movement into an operative position within said feed path so that the cam surface means thereof is operable to be engaged by a nail shank advanced during the feeding stroke of said feeding pawl to move said feeding pawl out of And back into said operative position and the nail shank engaging surface means of said holding pawl is operable to engage the nail shank and prevent rearward movement of the leading portion of the fastener package during the return stroke of said feeding pawl in which the cam surface means thereof is operable to engage a nail shank and move said feeding pawl out of and back into said operative position.
 10. A fastener driving device as defined in claim 9 including holding pawl means for engaging the upper surface of a nail head in response to the movement of a nail into said feed position for preventing upward movement of said nail with said fastener driving element out of said feed position during the return stroke of said fastener driving element.
 11. A fastener driving device comprising a housing structure, means defining a vertically extending drive track in said housing structure, a fastener driving element mounted in said drive track for vertical sliding movement through successive cycles including a downward drive stroke and an upward return stroke, means for feeding successive fasteners forwardly into said drive track to be driven outwardly thereof into a workpiece by said fastener driving element during the drive stroke thereof, means defining a cylindrical drive chamber in said housing structure, said cylindrical chamber being disposed in upwardly and rearwardly spaced relation to said drive track and having its axis extending upwardly and rearwardly from a point of intersection with the axis of said drive track which defines an obtuse angle therebetween, a drive piston slidably mounted within said cylindrical chamber for reciprocating movement through successive cycles including a drive stroke and a return stroke, and an elongated link having one end pivotally connected with said piston about an axis fixed with respect to said link and said piston and the other end pivotally connected with said fastener driving element aobut a parallel axis fixed with respect to said link and said fastener driving element for effecting movement of said fastener driving element through its drive stroke in response to the movement of said piston through its drive stroke at a speed which decreases and with a force which increases with respect to the speed and force of said piston drive stroke as the fastener driving element approaches the completion of the drive stroke, said piston and said housing structure each having a portion fixed with respect thereto, said fixed portions having opposed surface means facing toward one another spaced apart a predetermined distance when said piston is disposed in a position corresponding to the completion of said drive stroke, a compressible member of resilient material having first surface means facing in a direction opposed to the surface means of one of said fixed portions and disposed in engagement therewith and second surface means facing in the opposite direction, compressing means for engaging the surface means of the other of said fixed portions in response to the completion of the drive stroke of said piston and means mounting said compressing means with respect to said one fixed portion in a normal position of engagement with the second surface means of said compressible member in which the latter is compressed between said compressing means and said one fixed portion and for movement from said normal position toward said one fixed portion to further compress said compressible member therebetween in response to the interengagement of the surface means of said compressing means and said other fixed portion at the completion of the drive stroke of said piston.
 12. A fastener driving device as defined in claim 11 wherein said fastener feeding means is adapted to feed a fastener package of the type including a multiplicity of headed nails disposed with their shanks in generally parallel relation and interconnected in series by means permitting successive leading nails to be severed from the package and comprises means for supportinG the leading portion of said fastener package beneath the heads thereof for forward movement along a feed path in which the leading nail is moved into a severing position disposed rearwardly adjacent said drive track, said fastener driving element having a downwardly facing lower surface for engaging the head of a nail disposed in said drive track and driving the engaged nail outwardly of the drive track into a workpiece during the drive stroke of said fastener driving element, a rearwardly facing surface extending upwardly from said lower surface for engaging the leading surface of a nail disposed in said severing position and a downwardly facing upper surface extending rearwardly from the upper end of said rearwardly facing surface in vertically spaced relation to said lower surface for engaging the head of a nail disposed in said severing position and moving the engaged nail from said severing position downwardly into a feed position during the drive stroke of said fastener driving element, means engageable with nail shanks in the leading portion of said package for advancing successive leading nails of the package into said severing position to be moved therefrom by said fastener driving element during the drive stroke thereof into said feed position, and means engageable with the nail in said feed position for moving the latter forwardly into a drive position within said drive track so as to be driven outwardly thereof into a workpiece by said fastener driving element during the drive stroke.
 13. A fastener driving device as defined in claim 12 wherein said means engageable with the nail in said feed position comprises a nail feeding member mounted in said housing structure for movement through successive cycles including a feed stroke and a return stroke, said nail feeding member being biased to move through said feed stroke and having a cam surface engageable by said fastener driving element during the drive stroke thereof for effecting the return stroke of said nail feeding member, said means for advancing successive leading nails into said severing position comprising a feeding pawl and a holding pawl each having forwardly facing nail shank engaging surface means and inclined rearwardly facing cam surface means, means mounting said feeding pawl on said nail feeding member for movement through feed and return strokes with said nail feeding member and for biased movement with respect to said nail feeding member into an operative position within said feed path so that the nail engaging surface means thereof is operable to engage a nail shank and effect movement of the leading nail into said severing position during the feed stroke thereof, and means mounting said holding pawl on said housing structure for biased movement into an operative position within said feed path so that the cam surface means thereof is operable to be engaged by a nail shank advanced during the feeding stroke of said feeding pawl to move said feeding pawl out of and back into said operative position and the nail shank engaging surface means of said holding pawl is operable to engage the nail shank and prevent rearward movement of the leading portion of the fastener package during the return stroke of said feeding pawl in which the cam surface means thereof is operable to engage a nail shank and move said feeding pawl out of and back into said operative position.
 14. A fastener driving device as defined in claim 13 including holding pawl means for engaging the upper surface of a nail head in response to the movement of a nail into said feed position for preventing upward movement of said nail with said fastener driving element out of said feed position during the return stroke of said fastener driving element.
 15. A fastener driving device as defined in claim 11 wherein said link is connected with said piston by means including an elongated piston rod member fixedly connected at one end with said piston and pivoted to said link at the other end, said housing structure including means defIning a guidway for receiving said piston rod member including a straight elongated guide surface facing downwardly and rearwardly and roller means journaled on said piston rod member in a position to roll on said guide surface.
 16. A fastener driving device comprising a housing structure, means defining an elongated vertically extending drive track in said housing structure, means for receiving a fastener package of the type including a multiplicity of headed nails disposed with their shanks in generally parallel relation and interconnected in series by means permitting successive leading nails to be severed from the package and for supporting a leading portion of said fastener package beneath the heads thereof for forward movement along a feed path in which the leading nail is moved into a severing position disposed rearwardly adjacent said drive track, an elongated fastener driving element slidably mounted in said drive track for downward movement through a drive stroke and for upward movement through a return stroke, said fastener driving element having a downwardly facing lower surface for engaging the head of a nail disposed in said drive track and driving the engaged nail outwardly of the drive track into a workpiece during the drive stroke of said fastener driving element, a rearwardly facing surface extending upwardly from said lower surface for engaging the leading surface of a nail disposed in said severing position, and a downwardly facing upper surface extending rearwardly from the upper end of said rearwardly facing surface in vertically spaced relation to said lower surface for engaging the head of a nail disposed in said severing position and moving the engaged nail from said severing position downwardly into a feed position during the drive stroke of said fastener driving element, power operated means carried by said housing structure for effecting the drive stroke and return stroke of said fastener driving element, nail package advancing means engageable with successive nail shanks in the leading portion of said package and movable through successive feed strokes for advancing successive leading nails of the package into said severing position to be moved therefrom by said fastener driving element during the drive stroke thereof into said feed position in severed relation from the package, and severed nail feeding means engageable with successive severed nails in said feed position and movable through successive feed strokes simultaneously with the feed strokes of said nail package advancing means for moving successive severed nails forwardly into a drive position within said drive track so as to be driven outwardly thereof into a workpiece by said fastener driving element during the drive stroke thereof.
 17. A fastener driving device comprising a housing structure, means defining an elongated vertically extending drive track in said housing structure, means for receiving a fastener package of the type including a multiplicity of headed nails disposed with their shanks in generally parallel relation and interconnected in series by means permitting successive leading nails to be severed from the package and for supporting a leading portion of said fastener package beneath the heads thereof for forward movement along a feed path in which the leading nail is moved into a severing position disposed rearwardly adjacent said drive track, an elongated fastener driving element slidably mounted in said drive track for downward movement through a drive stroke and for upward movement through a return stroke, said fastener driving element having a downwardly facing lower surface for engaging the head of a nail disposed in said drive track and driving the engaged nail outwardly of the drive track into a workpiece during the drive stroke of said fastener driving element, a rearwardly facing surface extending upwardly from said lower surface for engaging the leading surface of a nail disposed in said severing position, and a downwardly facing upper surface extending rearwaRdly from the upper end of said rearwardly facing surface in vertically spaced relation to said lower surface for engaging the head of a nail disposed in said severing position and moving the engaged nail from said severing position downwardly into a feed position during the drive stroke of said fastener driving element, power operated means carried by said housing structure for effecting the drive stroke and return stroke of said fastener driving element, means engageable with nail shanks in the leading portion of said package for advancing successive leading nails of the package into said severing position to be moved therefrom by said fastener driving element during the drive stroke thereof into said feed position, and means engageable with the nail in said feed position for moving the latter forwardly into a drive position within said drive track so as to be driven outwardly thereof into a workpiece by said fastener driving element during the drive stroke thereof, said means engageable with the nail in said feed position comprising a nail feeding member mounted in said housing structure for movement through successive cycles including a feed stroke and a return stroke, said nail feeding member being biased to move through said feed stroke and having a cam surface engageable by said fastener driving element during the drive stroke thereof for effecting the return stroke of said nail feeding member, said means for advancing successive leading nails into said severing position comprising a feeding pawl and a holding pawl each having forwardly facing nail shank engaging surface means and inclined rearwardly facing cam surface means, means mounting said feeding pawl on said nail feeding member for movement through feed and return strokes with said nail feeding member and for biased movement with respect to said nail feeding member into an operative position within said feed path so that the nail engaging surface means thereof is operable to engage a nail shank and effect movement of the leading nail into said severing position during the feed stroke thereof, and means mounting said holding pawl on said housing structure for biased movement into an operative position within said feed path so that the cam surface means thereof is operative to be engaged by a nail shank advanced during the feed stroke of said feeding pawl so as to move said holding pawl out of and back into said operative position and the nail shank engaging surface means of said holding pawl is operable to engage the nail shank and prevent rearward movement of the leading portion of the fastener package during the return stroke of said feeding pawl and in which the cam surface means thereof is operable to engage a nail shank and move said feeding pawl out of and back into said operative position.
 18. A fastener driving device as defined in claim 17 including holding pawl means for engaging the upper surface of a nail head in response to the movement of a nail into said feed position for preventing upward movement of said nail with said fastener driving element out of said feed position during the return stroke of said fastener driving element.
 19. A fastener driving device as defined in claim 18 wherein said means for supporting the leading portion of the fastener package beneath the heads thereof includes a pair of rollers and means mounting said rollers for rotational movement about laterally spaced vertically extending axes, said rollers including peripheral surfaces for engaging the nail shanks and upwardly facing annular surfaces for engaging beneath the nail heads.
 20. A fastener driving device as defined in claim 19 wherein said roller mounting means includes a mounting arm assembly for each roller, said mounting arm assemblies having means for resiliently biasing said rollers for movement toward one another.
 21. A fastener driving device a housing structure, means defining an elongated vertically extending drive track in said housing structure, means for receiving a fastener package of the tYpe including a multiplicity of headed nails disposed with their shanks in generally parallel relation and interconnected in series by means permitting successive leading nails to be severed from the package and for supporting a leading portion of said fastener package beneath the heads thereof for forward movement along a feed path in which the leading nail is moved into a severing position disposed rearwardly adjacent said drive track, an elongated fastener driving element slidably mounted in said drive track for downward movement through a drive stroke and for upward movement through a return stroke, said fastener driving element having a downwardly facing lower surface for engaging the head of a nail disposed in said drive track and driving the engaged nail outwardly of the drive track into a workpiece during the drive stroke of said fastener driving element, a rearwardly facing surface extending upwardly from said lower surface for engaging the leading surface of a nail disposed in said severing position, and a downwardly facing upper surface extending rearwardly from the upper end of said rearwardly facing surface in vertically spaced relation to said lower surface for engaging the head of a nail disposed in said severing position and moving the engaged nail from said severing position downwardly into a feed position during the drive stroke of said fastener driving element, power operated means carried by said housing structure for effecting the drive stroke and return stroke of said fastener driving element, means engageable with nail shanks in the leading portion of said package for advancing successive leading nails of the package into said severing position to be moved therefrom by said fastener driving element during the drive stroke thereof into said feed position, and means engageable with the nail in said feed position for moving the latter forwardly into a drive position within said drive track so as to be driven outwardly thereof into a workpiece by said fastener driving element during the drive stroke thereof, and holding pawl means separate from said nail moving means engageable with the nail in said feed position for engaging the upper surface of a nail head in response to the movement of a nail into said feed position for preventing upward movement of said nail with said fastener driving element out of said feed position during the return stroke of said fastener driving element.
 22. A fastener driving device comprising a housing structure, means defining an elongated vertically extending drive track in said housing structure, means for receiving a fastener package of the type including a multiplicity of headed nails disposed with their shanks in generally parallel relation and interconnected in series by means permitting successive leading nails to be severed from the package and for supporting a leading portion of said fastener package beneath the heads thereof for forward movement along a feed path in which the leading nail is moved into a severing position disposed rearwardly adjacent said drive track, an elongated fastener driving element slidably mounted in said drive track for downward movement through a drive stroke and for upward movement through a return stroke, said fastener driving element having a downwardly facing lower surface for engaging the head of a nail disposed in said drive track and driving the engaged nail outwardly of the drive track into a workpiece during the drive stroke of said fastener driving element, a rearwardly facing surface extending upwardly from said lower surface for engaging the leading surface of a nail disposed in said severing position, and a downwardly facing upper surface extending rearwardly from the upper end of said rearwardly facing surface in vertically spaced relation to said lower surface for engaging the head of a nail disposed in said severing position and moving the engaged nail from said severing position downwardly into a feed position during the drive stroke of said fastener driving element, poweR operated means carried by said housing structure for effecting the drive stroke and return stroke of said fastener driving element, means engageable with nail shanks in the leading portion of said package for advancing successive leading nails of the package into said severing position to be moved therefrom by said fastener driving element during the drive stroke thereof into said feed position, and means engageable with the nail in said feed position for moving the latter forwardly into a drive position within said drive track so as to be driven outwardly thereof into a workpiece by said fastener driving element during the drive stroke thereof, said means for supporting the leading portion of the fastener package beneath the heads thereof including a pair of rollers and means mounting said rollers for rotational movement about laterally spaced vertically extending axes, said rollers including peripheral surfaces for engaging the nail shanks and upwardly facing annular surfaces for engaging beneath the nail heads.
 23. A fastener driving device comprising a housing structure, means defining an elongated vertically extending drive track in said housing structure, means for receiving a fastener package of the type including a multiplicity of headed nails disposed with their shanks in generally parallel relation and interconnected in series by means permitting successive leading nails to be severed from the package and for supporting a leading portion of said fastener package beneath the heads thereof for forward movement along a feed path in which the leading nail is moved into a severing position disposed rearwardly adjacent said drive track, an elongated fastener driving element slidably mounted in said drive track for downward movement through a drive stroke and for upward movement through a return stroke, said fastener driving element having a downwardly facing lower surface for engaging the head of a nail disposed in said drive track and driving the engaged nail outwardly of the drive track into a workpiece during the drive stroke of said fastener driving element, a rearwardly facing surface extending upwardly from said lower surface for engaging the leading surface of a nail disposed in said severing position, and a downwardly facing upper surface extending rearwardly from the upper end of said rearwardly facing surface in vertically spaced relation to said lower surface for engaging the head of a nail disposed in said severing position and moving the engaged nail from said severing position downwardly into a feed position during the drive stroke of said fastener driving element, power operated means carried by said housing structure for effecting the drive stroke and return stroke of said fastener driving element, means engageable with nail shanks in the leading portion of said package for advancing successive leading nails of the package into said severing position to be moved therefrom by said fastener driving element during the drive stroke thereof into said feed position, and means engageable with the nail in said feed position for moving the latter forwardly into a drive position within said drive track so as to be driven outwardly thereof into a workpiece by said fastener driving element during the drive stroke thereof, said power operated means including means defining a cylindrical chamber and a piston mounted within said chamber for movement through successive operative cycles each including a drive stroke and a return stroke, said piston and said housing structure each have a portion fixed with respect thereto, said fixed portions having opposed surface means facing toward one another spaced apart a predetermined distance when said piston is disposed in a position corresponding to the completion of said drive stroke, a compressible member of resilient material having first surface means facing in a direction opposed to the surface means of one of said fixed portions and disposed in engagement therewith and second surface means facing in the opposite direction, coMpressing means for engaging the surface means of the other of said fixed portions in response to the completion of the drive stroke of said piston and means mounting said compressing means with respect to said one fixed portion in a normal position of engagement with the second surface means of said compressible member in which the latter is compressed between said compressing means and said one fixed portion and for movement from said normal position toward said one fixed portion to further compress said compressible member therebetween in response to the interengagement of the surface means of said compressing means and said other fixed portion at the completion of the drive stroke of said piston.
 24. A fastener driving device comprising a housing structure, means defining an elongated vertically extending drive track in said housing structure, means for receiving a fastener package of the type including a multiplicity of headed nails disposed with their shanks in generally parallel relation and interconnected in series by means permitting successive leading nails to be severed from the package and for supporting a leading portion of said fastener package beneath the heads thereof for forward movement along a feed path in which the leading nail is moved into a severing position disposed rearwardly adjacent said drive track, an elongated fastener driving element slidably mounted in said drive track for downward movement through a drive stroke and for upward movement through a return stroke, said fastener driving element having a downwardly facing lower surface for engaging the head of a nail disposed in said drive track and driving the engaged nail outwardly of the drive track into a workpiece during the drive stroke of said fastener driving element, a rearwardly facing surface extending upwardly from said lower surface for engaging the leading surface of a nail disposed in said severing position, and a downwardly facing upper surface extending rearwardly from the upper end of said rearwardly facing surface in vertically spaced relation to said lower surface for engaging the head of a nail disposed in said severing position and moving the engaged nail from said severing position downwardly into a feed position during the drive stroke of said fastener driving element, power operated means carried by said housing structure for effecting the drive stroke and return stroke of said fastener driving element, means engageable with nail shanks in the leading portion of said package for advancing successive leading nails of the package into said severing position to be moved therefrom by said fastener driving element during the drive stroke thereof into said feed position, and means engageable with the nail in said feed position for moving the latter forwardly into a drive position within said drive track so as to be driven outwardly thereof into a workpiece by said fastener driving element during the drive stroke thereof, said housing structure including a pair of side members fixed together in side-by-side relation, one of said side members extending downwardly below the other of said side members, an access member mounted for movement into and out of an operative position disposed in cooperating side-by-side relation to said one side member below the other side member, said means defining said drive track including cooperating interior surfaces formed in said pair of side members and said access member, the portion of said interior surfaces formed in said access member being such that when said access member is disposed out of said operative position lateral access is provided to the portion of the drive track into which successive fasteners are fed by said fastener feeding means, said means for supporting the leading portion of the fastener package beneath the heads thereof comprising an elongated upwardly facing shoulder formed by a groove in the interior surface of said one side member below the other side member, said housing structure further including a second access meMber mounted for movement between an operative position in side-by-side relation to said one side member and below and rearwardly of said other side member and said first-mentioned access member respectively and an access position permitting lateral access to said elongated shoulder, and means for releasably retaining said second access member in its operative position and for retaining said first-mentioned access member in its operative position when said second access member is disposed in its operative position.
 25. A fastener driving device comprising a housing structure, means defining a cylindrical drive chamber in said housing structure, a drive piston slidably mounted within said drive chamber for reciprocating movement through successive operative cycles each including a drive stroke and a return stroke, means defining a drive track within said housing structure for receiving successive fasteners therein, a fastener driving element slidably mounted in said drive track and operatively connected with said drive piston for movement through a drive stroke to drive a fastener within said drive track outwardly thereof into a workpiece in response to the movement of said piston through its drive stroke and through return stroke in response to the movement of said piston through its return stroke, said piston and said housing structure each having a portion fixed with respect thereto, said portions having opposed surface means facing toward one another spaced apart a predetermined distance when said piston is disposed in a portion corresponding to the completion of said drive stroke, a compressible member of resilient material having first surface means facing in a direction opposed to the surface means of one of said portions and disposed in engagement therewith and second surface means facing in the opposite direction, compressing means for engaging the surface means of the other of said portions in response to the completion of the drive stroke of said piston, and means mounting said compressing means with respect to said one portion in a normal position of engagement with the second surface means of said compressible member in which the latter is compressed between said compressing means and said one portion and for movement from said normal position toward said one portion to further compress said compressible member therebetween in response to the interengagement of the surface means of said compressing means and said other portion at the completion of the drive stroke of said piston.
 26. A fastener driving device as defined in claim 25 wherein said one portion is fixed with respect to said piston. 